JP4966527B2 - Transparent silica sintered body and method for producing the same - Google Patents
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本発明は、従来から広く使われている透明石英ガラス製品の置き換えが可能な、比較的安価なシリカ粉を原料とし、セラミックス焼結体を製造するのに一般的に用いられている装置を用いて得られる、透明シリカ焼結体、およびその製造方法に関する。 The present invention is capable of replacing the transparent quartz glass products that are widely used conventionally, a relatively inexpensive silica powder as a raw material, are commonly used to produce ceramic sintered body apparatus Ru obtained using, transparency silica calcined body, and a manufacturing method thereof.
石英ガラスは、化学薬品容器、光学機器、分析・計測器具、各種半導体製造用治具などに幅広く用いられている。特に、光透過性を利用する分野において透明石英ガラス製品が幅広く用いられている。 Quartz glass is widely used in chemical containers, optical instruments, analysis / measurement instruments, various semiconductor manufacturing jigs, and the like. In particular, transparent quartz glass products are widely used in the field of utilizing light transmittance.
透明石英ガラス製品は一般に天然水晶等の原料を高温で溶融して製造され、その溶融状態での粘度が高いため、２１００℃以上に加熱して成形する必要がある。気泡の残留は透明性を損なうので、場合によっては真空チャンバー内で溶融して脱泡する工程が必要となることもある。その為、特殊な専用の加熱炉が必要であり、消費エネルギーが大きいので、製造コストが高くなる欠点を有している。更に、石英ガラスの塊をつくり、それを機械加工して所望の形状の製品を製造するので加工コストが高くなる欠点がある。 Transparent quartz glass products are generally produced by melting raw materials such as natural quartz at a high temperature, and since the viscosity in the molten state is high, it is necessary to mold by heating to 2100 ° C. or higher. Residual air bubbles impair transparency, and in some cases, a step of melting and defoaming in a vacuum chamber may be necessary. For this reason, a special dedicated heating furnace is required, and the energy consumption is large, so that the manufacturing cost is increased. Furthermore, since a lump of quartz glass is formed and machined to produce a product having a desired shape, there is a drawback that the processing cost is increased.
高純度の石英ガラスを製造するには、四塩化ケイ素等のガスを酸水素炎中もしくは酸素と混合して分解燃焼させ基材に堆積させる方法も知られているが、原料が高価なため製品も高価となり、石英ファイバー用石英ガラス等の不純物を嫌う用途に限定的に用いられているに過ぎない。また、この様にして作成した石英ガラスは、ハロゲン元素やＯＨ基を含むため軟化点が低く、耐熱性が必要な用途には使えなかった。 In order to produce high-purity quartz glass, a method is known in which a gas such as silicon tetrachloride is mixed with oxyhydrogen flame or oxygen and decomposed and burned to deposit it on the substrate. However, it is expensive and is used only for applications that do not like impurities such as quartz glass for quartz fiber. Further, the quartz glass prepared in this manner has a low softening point because it contains a halogen element or an OH group, and cannot be used for applications requiring heat resistance.
高純度の透明石英ガラスを得る方法として、ゾルゲル法によって高純度シリカ微粉を製造し（特許文献１）、それを原料とする溶融法や焼結法が検討されている。しかし、この方法においても、ゾルゲル法に用いるシリコン原料は高価であるし、ゾルゲル法によるシリカ粉製造法にはプロセス条件の緻密な制御や長時間の乾燥といったプロセス上の問題が存在する。 As a method for obtaining a high-purity transparent quartz glass, a high-purity silica fine powder is produced by a sol-gel method (Patent Document 1), and a melting method or a sintering method using this as a raw material has been studied. However, even in this method, the silicon raw material used in the sol-gel method is expensive, and the silica powder production method by the sol-gel method has process problems such as precise control of process conditions and long-time drying.
一方、シリカ粉を原料として、プレス成形（特許文献２）、鋳込み成形（非特許文献１、特許文献３）、押し出し成形（特許文献４）等の通常のセラミックス製造プロセスで用いられる成形体製造方法によって、シリカ粉成形体を作製し、その後、焼成して得る石英ガラス焼結体の製造方法も検討されている。粉体成形によって製品に近い形の成形体を作り焼結して製品を得るので、機械加工の手間が軽減され、製造プロセスにおいて特殊な装置も不要なため、コスト低減が図れると言われているが、一般には、透明な焼結体を得るのは容易でない。 On the other hand, using a silica powder as a raw material, a molded body manufacturing method used in normal ceramic manufacturing processes such as press molding (Patent Document 2), cast molding (Non-Patent Document 1, Patent Document 3), and extrusion molding (Patent Document 4). Thus, a method for producing a quartz glass sintered body obtained by producing a silica powder molded body and then firing it has been studied. It is said that since compacted products are made by powder molding and sintered to obtain products, the labor of machining is reduced, and no special equipment is required in the manufacturing process, thus reducing costs. However, in general, it is not easy to obtain a transparent sintered body.
一般的な成型方法では、透明な焼結体を得るのに不可欠な、高い密度や均一性を有する成形体を得にくく、従って、残留気泡の少ない透明な焼結体を得るために、真空中やヘリウムと塩素の混合ガス気流中で長時間焼成したり、更に１７００〜１８５０℃で溶融したり、水素ガス中で１７００℃で焼成する等、製造プロセス上の様々な工夫が必要であった。 In general molding methods, it is difficult to obtain a molded body having high density and uniformity, which is indispensable for obtaining a transparent sintered body. Therefore, in order to obtain a transparent sintered body with few residual bubbles, Various measures on the manufacturing process were required, such as firing for a long time in a mixed gas stream of helium and chlorine, further melting at 1700 to 1850 ° C., and firing at 1700 ° C. in hydrogen gas.
また、本願発明者らは、粒度の異なる市販の球状シリカ粉を配合して用い、成型方法を工夫し、成形体の密度と均一性を高め、透光性のあるシリカ焼結体を得たが、光の透過率、特に波長が４００ｎｍ以下の紫外光領域の透過率は、不十分であった（非特許文献２）。 Further, the inventors of the present invention blended and used commercially available spherical silica powders having different particle sizes, devised the molding method, increased the density and uniformity of the molded body, and obtained a translucent silica sintered body. However, the transmittance of light, particularly the transmittance in the ultraviolet region having a wavelength of 400 nm or less, was insufficient (Non-Patent Document 2).
従来から用いられている、または検討されてきた透明石英ガラスの製造方法は、特殊な装置が必要だったり、特別に調整したシリカ原料粉を用いたり、製造条件の精密な制御が必要だったり、加工コストがかかり、いずれも製造コストが高くなるという課題があった。加えて、焼結法で透明石英ガラスを得るためには、原料シリカ粉、成形法、焼結法すべてにわたる技術改良が必要であり、特に、この用途に使える入手が容易な原料シリカ粉が見いだせていないという問題があった。 The production method of transparent quartz glass that has been used or has been studied conventionally requires special equipment, uses specially prepared silica raw material powder, requires precise control of production conditions, There was a problem that the processing cost was high and both of them were high in manufacturing cost. In addition, in order to obtain transparent quartz glass by the sintering method, it is necessary to improve the technology for all of the raw silica powder, the molding method, and the sintering method. In particular, an easily available raw silica powder that can be used for this purpose can be found. There was a problem that not.
透明焼結体の原料として用いるシリカ粉は、微細で粒径のそろった球状シリカ粉が好ましいとの考え方から、例えば、ゾルゲル法によって得たシリカ粉を使用することが検討されたが、ゾルゲル法で製造したシリカ粉はその表面にシラノール基が多く付着しており、それが気泡や失透の原因となるため、昇温過程で水分が含まれない十分に乾燥した雰囲気あるいは高真空雰囲気で焼成しなければならないという課題があった。一方、工業的に得られる安価なシリカ粉を用いると、焼結体に気泡が残留しやすく、あるいは失透しやすく、光の透過率が低いという課題がある。 The silica powder used as the raw material of the transparent sintered body is considered to be a silica powder obtained by a sol-gel method, for example, from the idea that a fine and uniform spherical silica powder is preferred. The silica powder produced in the process has many silanol groups attached to its surface, which causes bubbles and devitrification, so it is fired in a sufficiently dry or high-vacuum atmosphere that does not contain moisture during the heating process. There was a problem that had to be done. On the other hand, when inexpensive silica powder obtained industrially is used, there is a problem that bubbles are likely to remain in the sintered body or are easily devitrified, and the light transmittance is low.
本発明の目的は、これらの従来技術の有する課題を解決して、様々な分野で使用可能な、透明性に優れる、安価な透明シリカ焼結体とその製造方法を提供することにある。 An object of the present invention is to solve these problems of the prior art and provide an inexpensive transparent silica sintered body that is excellent in transparency and can be used in various fields, and a method for producing the same.
本発明者は、各種のシリカ粉を用いて、セラミックスの分野で用いられている各種成形体製造技術や焼結技術を用いながら、各種条件を実験的に検討し、多くの組み合わせの中から、透明シリカ焼結体が容易に得られる条件を見いだし、また、得られた透明シリカ焼結体が優れた特性を持つことを見いだし、本発明を完成した。 The present inventor uses various silica powders to experimentally examine various conditions while using various molded body manufacturing techniques and sintering techniques used in the field of ceramics, and from among many combinations, The inventors have found the conditions under which a transparent silica sintered body can be easily obtained, and have found that the obtained transparent silica sintered body has excellent characteristics, thereby completing the present invention.
即ち、本発明は、１５μｍ以上の粗大粒子数が５０個／ｇ以下かつ１５μｍ以上の金属粒子数が１個／ｇ以下で、平均粒子径が０．１〜２μｍ、比表面積が２〜３０ｍ2／ｇであり、しかも構成粒子が球状であるシリカ粉末をフロックキャスト成形した後に焼結してなる、相対密度が９９．８％以上であり、アルミニウム、鉄、ナトリウム、カルシウム、マグネシウムの酸化物換算の含有量がそれぞれ５０ｐｐｍ以下であり、波長が３５０ｎｍの紫外光の直線透過率が厚さ２ｍｍで８５％以上であることを特徴とする透明シリカ焼結体であり、好ましくは、原料として用いる球状のシリカ粉末が火炎溶融法で得られたものである。 That is, in the present invention, the number of coarse particles of 15 μm or more is 50 particles / g or less and the number of metal particles of 15 μm or more is 1 particle / g or less , the average particle diameter is 0.1 to 2 μm, and the specific surface area is 2 to 30 m 2. / G and silica powder with spherical constituent particles formed by flock casting and then sintered, the relative density is 99.8% or more, and converted to oxides of aluminum, iron, sodium, calcium, magnesium content is not more 50ppm or less, Ri transparent silica sintered der, wherein the wavelength is not less than 85% in-line transmission of a thickness of 2mm of the ultraviolet light 350 nm, good Mashiku the starting The spherical silica powder used as is obtained by the flame melting method.
また、本発明は、１５μｍ以上の粗大粒子数が５０個／ｇ以下かつ１５μｍ以上の金属粒子数が１個／ｇ以下で、平均粒子径が０．１〜２μｍ、比表面積値が２〜３０ｍ2／ｇであり、アルミニウム、鉄、ナトリウム、カルシウム、マグネシウムの酸化物換算の含有量がそれぞれ５０ｐｐｍ以下の球状シリカ粉末を、フロックキャスト成形法により、相対密度が６０％以上の成形体とし、得られた成形体を１３００℃以上１６００℃以下の温度範囲で焼結することを特徴とする透明シリカ焼結体の製造方法である。 In the present invention, the number of coarse particles of 15 μm or more is 50 particles / g or less and the number of metal particles of 15 μm or more is 1 particle / g or less , the average particle diameter is 0.1 to 2 μm, and the specific surface area value is 2 to 30 m. 2 / g, and spherical silica powders each containing 50 ppm or less in terms of oxides of aluminum, iron, sodium, calcium, and magnesium are formed into a molded body having a relative density of 60% or more by a flock cast molding method. The obtained molded body is sintered in a temperature range of 1300 ° C. or higher and 1600 ° C. or lower.
本発明は、特定の粒度分布、比表面積値、不純物量を有するシリカ粉を原料として用いることで、通常のセラミックス製品を製造するプロセスと同様の装置を用いて透明シリカ焼結体を製造でき、更に、製品形状を得るための外形の機械加工に掛かる手間を大幅に低減した安価で透明性に優れる透明シリカ焼結体を提供するものである。本発明の透明シリカ焼結体は、ハロゲン不純物を含まず、ＯＨ基の含有量、不純物量、気泡の数も少ないので、軟化点が高く、また、紫外から赤外までの広い範囲で透明性が高いため、各種治具類や耐熱材料、光学材料に好適に使用できる。 The present invention uses a silica powder having a specific particle size distribution, a specific surface area value, and an impurity amount as a raw material, so that a transparent silica sintered body can be produced using an apparatus similar to a process for producing a normal ceramic product, Furthermore, the present invention provides a transparent silica sintered body which is inexpensive and excellent in transparency, which greatly reduces the labor required for machining the outer shape to obtain a product shape. The transparent silica sintered body of the present invention does not contain halogen impurities, has a low OH group content, a small amount of impurities, and a small number of bubbles, so has a high softening point and is transparent in a wide range from ultraviolet to infrared. Therefore, it can be suitably used for various jigs, heat-resistant materials, and optical materials.
本発明の透明シリカ焼結体の製造方法は、ハロゲン不純物を含まず、ＯＨ基の含有量、不純物量、気泡の数も少ないので、軟化点が高く、また、紫外から赤外までの広い範囲で透明性が高い透明シリカ焼結体を、安定して、歩留まり高く提供できる特徴がある。 The method for producing a transparent silica sintered body according to the present invention does not contain halogen impurities, has a low OH group content, an impurity amount, and a small number of bubbles, and thus has a high softening point and a wide range from ultraviolet to infrared. The transparent silica sintered body having high transparency can be provided stably and with a high yield.
本発明の透明シリカ焼結体は、波長が３５０ｎｍの紫外光の直線透過率が厚さ２ｍｍで６０％以上である特徴を有するが、火炎溶融法等の乾式合成シリカ粉を原料として得られる従来公知の透明シリカ焼結体のこの数値は高々５０％であるので、従来得られなかった透明性（光透過性）を有し、特に、紫外光の透過を必要とする、例えば光学部品等へのいろいろな用途に好適である。 The transparent silica sintered body of the present invention has a characteristic that the linear transmittance of ultraviolet light having a wavelength of 350 nm is 60% or more at a thickness of 2 mm, but is conventionally obtained using a dry synthetic silica powder such as a flame melting method as a raw material. Since this numerical value of the known transparent silica sintered body is 50% at most, it has transparency (light transmittance) that has not been obtained so far, and particularly, for example, for optical parts that require ultraviolet light transmission. It is suitable for various uses.
本発明は、１５μｍ以上の粗大粒子数が３００個／ｇ以下で、平均粒子径が０．１〜２μｍ、比表面積が２〜３０ｍ2／ｇであり、しかも構成粒子が球状であるシリカ粉末をキャスト成形した後に焼結してなる、アルミニウム、鉄、ナトリウム、カルシウム、マグネシウムの酸化物換算の含有量がそれぞれ５０ｐｐｍ以下であり、波長が３５０ｎｍの紫外光の直線透過率が厚さ２ｍｍで６０％以上、好ましくは７０％以上であることを特徴とする透明シリカ焼結体である。 The present invention provides a silica powder in which the number of coarse particles of 15 μm or more is 300 particles / g or less, the average particle diameter is 0.1 to 2 μm, the specific surface area is 2 to 30 m 2 / g, and the constituent particles are spherical. Aluminum, iron, sodium, calcium, and magnesium oxide-converted contents that are sintered after cast molding are each 50 ppm or less, and the linear transmittance of ultraviolet light having a wavelength of 350 nm is 60% at a thickness of 2 mm. Thus, the transparent silica sintered body is preferably 70% or more.
本発明に用いるシリカ粉は、１５μｍ以上の粗大粒子数が３００個／ｇ以下で、平均粒子径が０．１〜２μｍ、比表面積が２〜３０ｍ2／ｇであり、しかも構成粒子が球状であるシリカ粉末である。これらの範囲を外れると、いずれの場合も成形性が悪くなって成形密度の低下や均一性の低下が起こり、ひいては、焼結体中に気泡が残留し、密度低下や透明性の低下が起こる等、焼結体特性に悪影響を及ぼす。１５μｍ以上の粗大粒子数が１００個／ｇ以下であると、焼結体の相対密度が９９．５％以上で、残留気泡が少なく、紫外光（波長が３５０ｎｍ）の直線透過率が厚さ２ｍｍでが７０％以上である焼結体が得られるので、更に好ましい。 The silica powder used in the present invention has a number of coarse particles of 15 μm or more of 300 particles / g or less, an average particle size of 0.1 to 2 μm, a specific surface area of 2 to 30 m 2 / g, and constituent particles are spherical. A silica powder. Outside these ranges, in any case, the moldability deteriorates and the molding density decreases and the uniformity decreases. As a result, bubbles remain in the sintered body, resulting in a decrease in density and a decrease in transparency. Adversely affects the properties of the sintered body. When the number of coarse particles of 15 μm or more is 100 particles / g or less, the relative density of the sintered body is 99.5% or more, there are few residual bubbles, and the linear transmittance of ultraviolet light (wavelength is 350 nm) is 2 mm thick. It is more preferable because a sintered body having a thickness of 70% or more can be obtained.
原料シリカ粉として構成粒子が球状のものからなる、いわゆる球状粉末を使用すると、スラリー粘度を下げることが出来、その結果、高い成形体密度を得ることができるので、焼結体中への気泡の残留を減らすことが出来る。「球状」の程度としては、平均球形度が０．９０以上であることが好ましく、特に０．９５以上であることが好ましい。平均球形度が大きくなると、転がり抵抗が少なくなるので成形性、充填性が高まり、高い成形体密度を得ることができる。 When using so-called spherical powder composed of spherical particles as raw material silica powder, the slurry viscosity can be lowered, and as a result, a high molded body density can be obtained. Residue can be reduced. As the degree of “spherical”, the average sphericity is preferably 0.90 or more, and particularly preferably 0.95 or more. When the average sphericity is increased, the rolling resistance is decreased, so that the moldability and filling property are improved, and a high molded body density can be obtained.
焼結体製造に用いるシリカ粉中に含まれる不純物は、シリカ焼結体の失透の原因となり、また焼結体が紫外光を吸収する原因となるので、アルミニウム、鉄、ナトリウム、カルシウム、マグネシウムの酸化物換算の含有量がそれぞれ５０ｐｐｍ以下である必要があり、２０ｐｐｍ以下であることが好ましい。成形、焼成工程でこれらの不純物が混入しないように、使用する機器の材質や作業環境等に注意を払う必要がある。そうすることにより、得られる焼結体中のこれらの不純物量は、使用するシリカ粉中の不純物量とほぼ同じ量となる。 Impurities contained in the silica powder used in the production of the sintered body cause devitrification of the silica sintered body and cause the sintered body to absorb ultraviolet light. Therefore, aluminum, iron, sodium, calcium, magnesium It is necessary that the content in terms of oxides is 50 ppm or less, and preferably 20 ppm or less. It is necessary to pay attention to the material of the equipment used and the work environment so that these impurities are not mixed in the molding and firing processes. By doing so, the amount of these impurities in the obtained sintered body becomes almost the same as the amount of impurities in the silica powder to be used.
不純物が金属粒子として含まれる場合は、金属粒子表面を起点として結晶化が進むため失透の原因になりやすく、また、光透過率を低下させるので、１５μｍ以上の金属粒子が１０個／ｇ以下であることが好ましい。 When impurities are contained as metal particles, crystallization proceeds from the metal particle surface, which is likely to cause devitrification, and the light transmittance is reduced, so that the number of metal particles of 15 μm or more is 10 particles / g or less. It is preferable that
更に、原料シリカ粉は、結晶質シリカ粉末又は合成シリカ粉末を火炎処理（火炎溶融法）して球状化した非晶質シリカ粉であることが好ましい。火炎処理して得た球状シリカ粉は、湿式法で製造したシリカ粉に比べて表面のシラノール基が少ないので、シラノール基を除くための真空加熱処理等の必要が無く、大気中の焼成で容易に透明シリカ焼結体を得ることができるため好ましい。製造方法の詳細については後述する。 Further, the raw silica powder is preferably an amorphous silica powder obtained by spheroidizing a crystalline silica powder or a synthetic silica powder by flame treatment (flame melting method). Spherical silica powder obtained by flame treatment has less silanol groups on the surface compared to silica powder produced by a wet process, so there is no need for vacuum heat treatment to remove silanol groups, and it is easy to burn in air Since a transparent silica sintered body can be obtained, it is preferable. Details of the manufacturing method will be described later.
シリカ成形体を作製するには、まず、原料シリカ粉に水と分散剤を加えてスラリーを作製する。水と分散剤の添加量は、事前に湿潤点と流動点を測定し、十分に高い濃度と十分に低い粘度のスラリーが得られるように決める。湿潤点と流動点が最も小さくなる分散剤の添加量が、好ましい分散剤の添加量である。分散剤は市販の分散剤を用いればよいが、燐酸ナトリウムのような無機系イオンを含む分散剤はなるべく避けるほうがよい。 In order to prepare a silica molded body, first, slurry is prepared by adding water and a dispersant to raw silica powder. The amounts of water and dispersant added are determined in advance so as to obtain a slurry having a sufficiently high concentration and a sufficiently low viscosity by measuring the wet point and the pour point in advance. The addition amount of the dispersant having the smallest wet point and pour point is a preferable addition amount of the dispersant. A commercially available dispersant may be used as the dispersant, but a dispersant containing inorganic ions such as sodium phosphate should be avoided as much as possible.
なお、湿潤点と流動点を求めるには、一定量のシリカ粉をガラス板上に取り、上部からビュレットを用いてイオン交換水を滴下し、へらで練りながら、粉全体がペースト状の塊になる時の水の量を測定し湿潤点とする。更に滴下し、ペーストが流動化する水の量を測定し流動点とする。 In order to obtain the wet and pour points, a certain amount of silica powder is taken on a glass plate, ion-exchanged water is dropped from above using a burette, and the whole powder is made into a paste-like lump while kneading with a spatula. Measure the amount of water at that time and use it as the wetting point. Furthermore, it dripped and the quantity of the water which a paste fluidizes is measured, and it is set as a pour point.
水の添加量は、湿潤点と流動点を参考にして、採用する成形法に適したスラリーになるように決める。水としては不純物イオンの少ないイオン交換水を使用するのが好ましい。 The amount of water to be added is determined so as to obtain a slurry suitable for the molding method to be employed with reference to the wet point and pour point. It is preferable to use ion-exchanged water with few impurity ions as water.
スラリーの作製には、ボールミル、自公転式混練機、等を用いることが出来る。得られたスラリーを真空に引いて脱泡した後、型に入れて成形する。型の材質は何でも使用できるが、金属ないし金属イオン不純物の混入のない樹脂製のものが望ましい。また、遠心機にかけて成形すると複雑形状の成形体を得ることができ、また、スラリーを型へ流し込む時に発生する気泡の除去、成形体の一層の密度向上に役立つので好ましい。 For the production of the slurry, a ball mill, a self-revolving kneader, or the like can be used. The resulting slurry is degassed by applying a vacuum, and then placed in a mold and molded. Any material can be used for the mold, but it is preferable to use a resin that does not contain metal or metal ion impurities. Further, it is preferable to form with a centrifuge because a molded body having a complicated shape can be obtained, and it is useful for removing bubbles generated when the slurry is poured into a mold and further improving the density of the molded body.
成形体を得るための成形方法としては、高い成形体密度が得られる点で優れているキャスト法を採用する。更に、流し込み鋳込み、固形鋳込み、振動鋳込み、等の各種のキャスト法を用いることが可能であるが、中でもフロックキャスト法が、高い密度と高い均一性を持つ成形体が得られるので好ましい。フロックキャスト成形では、スラリーを入れた型を加熱することにより固形化し、その後、乾燥して型から成形体を取りだす。この際、加熱と共に、振動や遠心力を加えたりすることもある。 As a molding method for obtaining a molded body, a casting method that is excellent in that a high molded body density is obtained is adopted. Further, it is possible to use various casting methods such as casting, solid casting, vibration casting, etc. Among them, the flock casting method is preferable because a molded body having high density and high uniformity can be obtained. In the flock cast molding, the mold containing the slurry is solidified by heating and then dried to take out the molded body from the mold. At this time, vibration or centrifugal force may be applied together with heating.
次に、成形体を１３００℃以上、１６００℃以下の温度で、１０分から６時間程度焼成すると、透明シリカ焼結体が得られる。焼成時の雰囲気は、真空等を適用することも勿論可能ではあるが、経済性の観点から常圧の空気が好ましい。 Next, when the molded body is fired at a temperature of 1300 ° C. or higher and 1600 ° C. or lower for about 10 minutes to 6 hours, a transparent silica sintered body is obtained. Of course, a vacuum or the like can be applied to the atmosphere during firing, but atmospheric pressure is preferable from the viewpoint of economy.
以下、各種測定法について説明する。 Hereinafter, various measurement methods will be described.
粗大粒子、金属粒子数の測定方法は、球状シリカ粉末１０ｇを５質量％水スラリーとして超音波分散処理後、１５μｍ目開きのナイロンメッシュにて吸引濾過し、篩上残分をマイクロスコープにて観察して、粗粒子数および金属粒子数をカウントする。着色し、金属光沢を持つ粒子は、金属粒子とした。 The method for measuring the number of coarse particles and metal particles is ultrasonic dispersion treatment using 10 g of spherical silica powder as a 5% by weight water slurry, suction filtration through a 15 μm opening nylon mesh, and the residue on the sieve is observed with a microscope. Then, the number of coarse particles and the number of metal particles are counted. The colored particles with metallic luster were metallic particles.
粉末の構成粒子の平均球形度は、実体顕微鏡（例えば「モデルＳＭＺ−１０型」ニコン社製）、走査型電子顕微鏡等にて撮影した粒子像を画像解析装置（例えば、日本アビオニクス社製など）に取り込み、次のようにして測定することができる。すなわち、写真から粒子の投影面積（Ａ）と周囲長（ＰＭ）を測定する。周囲長（ＰＭ）に対応する真円の面積を（Ｂ）とすると、その粒子の真円度はＡ／Ｂとして表示できる。そこで、試料粒子の周囲長（ＰＭ）と同一の周囲長を持つ真円を想定すると、ＰＭ＝２πｒ、Ｂ＝πｒ2であるから、Ｂ＝π×（ＰＭ／２π）2となり、個々の粒子の真円度は、真円度＝Ａ／Ｂ＝Ａ×４π／（ＰＭ）2として算出することができる。このようにして得られた任意の粒子３００個の真円度を求めその平均値を平均球形度とした。 The average sphericity of the constituent particles of the powder is determined by measuring the particle image taken with a stereomicroscope (for example, “Model SMZ-10” manufactured by Nikon Corporation) or a scanning electron microscope (for example, manufactured by Nippon Avionics Co., Ltd.) And can be measured as follows. That is, the projected area (A) and the perimeter (PM) of particles are measured from a photograph. When the area of a perfect circle corresponding to the perimeter (PM) is (B), the roundness of the particle can be displayed as A / B. Therefore, assuming a perfect circle having the same peripheral length as the sample particle (PM), PM = 2πr and B = πr 2 , so that B = π × (PM / 2π) 2 , and each particle The roundness can be calculated as roundness = A / B = A × 4π / (PM) 2 . The roundness of 300 arbitrary particles thus obtained was determined, and the average value was defined as the average sphericity.
平均粒子径は、レーザー回折光散乱法粒子径分布測定機（例えば、「モデルＬＳ−２３０」ベックマンコールター社製）にて測定する。測定に際しては、溶媒には水を用い、前処理として、１分間、ホモジナイザーを用いて２００Ｗの出力をかけて分散処理する。また、ＰＩＤＳ（Ｐｏｌａｒｉｚａｔｉｏｎ Ｉｎｔｅｎｓｉｔｙ Ｄｉｆｆｅｒｅｎｔｉａｌ Ｓｃａｔｔｅｒｉｎｇ）濃度を４５〜５５％になるように調製する。なお、水の屈折率には１．３３を用い、粉末の屈折率には文献値、例えば非晶質シリカでは１．５０を用いた。比表面積は、窒素ガス吸着によるＢＥＴ１点法により測定した。 The average particle size is measured with a laser diffraction light scattering particle size distribution measuring machine (for example, “Model LS-230” manufactured by Beckman Coulter, Inc.). In the measurement, water is used as a solvent, and as a pretreatment, dispersion treatment is performed for 1 minute using a homogenizer with an output of 200 W. Moreover, it prepares so that a PIDS (Polarization Intensity Differential Scattering) density | concentration may be 45-55%. The refractive index of water was 1.33, and the refractive index of the powder was a literature value, for example, 1.50 for amorphous silica. The specific surface area was measured by the BET one point method by nitrogen gas adsorption.
原料シリカ粉並びに透明シリカ焼結体についての不純物量については、発光分光分析法を用いて、アルミニウム、鉄、ナトリウム、カルシウム、マグネシウムの各々の元素の含有量を測定した後、酸化物換算して求める。 For the amount of impurities in the raw silica powder and the transparent silica sintered body, the content of each element of aluminum, iron, sodium, calcium, and magnesium is measured using an emission spectroscopic analysis method, and then converted into an oxide. Ask.
透明シリカ焼結体や原料シリカ粉の非晶質率については、粉末Ｘ線回折装置（例えば、「モデルＭｉｎｉ Ｆｌｅｘ」ＲＩＧＡＫＵ社製）を用い、ＣｕＫα線の２θが２６°〜２７．５°の範囲において試料のＸ線回折分析を行い、特定回折ピークの強度比から測定する。すなわち、結晶質シリカは２６．７°に主ピークが存在するが非晶質シリカでは存在しないので、両者が混在しているとその割合に応じた２６．７°のピーク高さが得られることを利用し、結晶質シリカ標準試料のＸ線強度に対する試料のＸ線強度の比を測定して、結晶質シリカ混在率（試料のＸ線回折強度／結晶質シリカのＸ線回折強度）を算出し、非晶質率（％）＝（１−結晶質シリカ混在率）×１００、から非晶質率を求める。 Regarding the amorphous ratio of the transparent silica sintered body and the raw silica powder, a powder X-ray diffractometer (for example, “Model Mini Flex” manufactured by RIGAKU) is used, and 2θ of CuKα ray is 26 ° to 27.5 °. An X-ray diffraction analysis of the sample is performed in the range and measured from the intensity ratio of the specific diffraction peak. That is, crystalline silica has a main peak at 26.7 °, but does not exist in amorphous silica, so if both are present, a peak height of 26.7 ° corresponding to the ratio can be obtained. Is used to measure the ratio of the X-ray intensity of the sample to the X-ray intensity of the crystalline silica standard sample, and to calculate the mixing ratio of the crystalline silica (X-ray diffraction intensity of the sample / X-ray diffraction intensity of the crystalline silica) Then, the amorphous ratio is obtained from the amorphous ratio (%) = (1-crystalline silica mixing ratio) × 100.
成形体の密度は、十分乾燥した後、重量と寸法を測定して、計算から求めた。焼結体の密度は、アルキメデス法で測定した。相対密度は、非晶質シリカの理論密度である２．２１ｇ／ｃｍ3を用いて算出した。 The density of the molded body was obtained by calculation after sufficiently drying and measuring the weight and dimensions. The density of the sintered body was measured by the Archimedes method. The relative density was calculated using 2.21 g / cm 3 , which is the theoretical density of amorphous silica.
焼結体の光透過率は、サンプルを厚さ２ｍｍに加工し、両面を研磨機（ＥＣＯＭＥＴ４，ＢＵＥＨＬＥＲ Ｃｏ．Ｌｔｄ．製）と３μｍ未満のダイヤモンドサスペンションを用いて鏡面研磨した。最終的な形状は縦６ｍｍ×横２０ｍｍ×厚さ２ｍｍとした。上記のように加工したサンプルに対して，厚さ２ｍｍの方向に垂直に光を通すようにして２００−１１００ｎｍの範囲の光透過率を紫外可視分光光度計（ＵＶ ｍｉｎｉ−１２４０，島津製作所製）を用いて測定した。 For the light transmittance of the sintered body, the sample was processed to a thickness of 2 mm, and both surfaces were mirror-polished using a polishing machine (ECOMET4, manufactured by BUEHLER Co. Ltd.) and a diamond suspension of less than 3 μm. The final shape was 6 mm long x 20 mm wide x 2 mm thick. Ultraviolet-visible spectrophotometer (UV mini-1240, manufactured by Shimadzu Corporation) has a light transmittance in the range of 200-1100 nm so that light is transmitted perpendicularly to the 2 mm thickness direction for the sample processed as described above. It measured using.
焼結体の構成相を調べるため、Ｘ線回折装置（ＭｕｌｔｉＦｌｅｘ，Ｒｉｇａｋｕ製）を用いた。更に、焼結体内部の粗大欠陥および失透の有無を確認するため、偏光顕微鏡（ＥＣＬＩＰＳＥ Ｅ６００ ＰＯＬ． Ｎｉｃｏｎ製）を用いて浸液透光法により観察した。焼結体の微構造は走査型電子顕微鏡（ＪＳＭ−５２００，日本電子製）により観察した。 In order to examine the constituent phases of the sintered body, an X-ray diffractometer (MultiFlex, manufactured by Rigaku) was used. Furthermore, in order to confirm the presence or absence of coarse defects and devitrification inside the sintered body, it was observed by an immersion liquid transmission method using a polarizing microscope (manufactured by ECLIPSE E600 POL. Nicon). The microstructure of the sintered body was observed with a scanning electron microscope (JSM-5200, manufactured by JEOL).
次に、本発明の原料として好ましく使用できるシリカ粉の製造方法について説明する。 Next, the manufacturing method of the silica powder which can be preferably used as a raw material of this invention is demonstrated.
原料粉末としては、シリコン金属粉又はシリカ粉を用い、火炎中に噴霧して酸化反応および溶融し球状化する。燃焼ガスと共に得られた球状シリカ粉末をコアンダブロックを有する気流分級機に導き、気流分級し、酸化反応の不十分な金属粒子や異常成長したり、一旦炉体に付着し剥離した粗大粒子等を分離除去する。コアンダブロックを有する気流分級機とは、飛散降下経路の差が粉末の粒径によって異なる現象（コアンダ現象）を利用するため、湾曲したブロックを備えさせ、その湾曲面に沿わせて気流を噴出させる構造の分級機のことであり（例えば特開平８−８９９００号公報）、市販機としては、例えば株式会社マツボー社製商品名「エルボージェット分級機」などがある。 As the raw material powder, silicon metal powder or silica powder is used and sprayed in a flame to oxidize and melt and spheroidize. The spherical silica powder obtained together with the combustion gas is guided to an air classifier having a Coanda block, and air stream classification is performed to remove insufficiently oxidized metal particles, abnormal growth, coarse particles once adhered to the furnace body, etc. Separate and remove. The air classifier with a Coanda block uses a phenomenon (Coanda phenomenon) in which the difference in the scattering path differs depending on the particle size of the powder (Coanda phenomenon). It is a classifier having a structure (for example, JP-A-8-89900), and examples of commercially available machines include “Elbow Jet Classifier” manufactured by Matsubo Corporation.
気流分級操作は、製造された球状金属酸化物粉末の回収前又は回収後のいずれであっても良いが、回収前のインライン分級であれば、球状酸化物微粒子合成時の火炎による燃焼ガス熱量が利用でき、分散状態も良く、より好ましい。気流の温度を１５０℃以上とすることにより水分による凝集を避けることが出来、気流分級機のコアンダブロック入り口における流速を５０ｍ／ｓ以上にすることで、分散性やコアンダ効果が高まり、分級効率をより高めることができる。流速はガス種の設定流量及び設定ガス温度から単位時間あたりに通過する体積が計算され、これをコアンダブロック入口の面積で除することによって流速を算出することができる。 The air classification operation may be performed either before or after the recovery of the produced spherical metal oxide powder, but if it is in-line classification before the recovery, the amount of combustion gas heat generated by the flame during the synthesis of the spherical oxide fine particles It can be used and the dispersion state is good and more preferable. Aggregation due to moisture can be avoided by setting the temperature of the airflow to 150 ° C. or higher, and by increasing the flow velocity at the Coanda block entrance of the airflow classifier to 50 m / s or more, the dispersibility and the Coanda effect are enhanced, and the classification efficiency is increased. Can be increased. The flow rate can be calculated by calculating the volume passing per unit time from the set flow rate and set gas temperature of the gas species and dividing this by the area of the Coanda block inlet.
（実施例１）
原料シリカ粉の作製
ＬＰＧ−酸素で形成された火炎中に金属シリコン粉末原料（平均粒子径１０μｍ）を連続的に供給する。火炎処理された生成物は、燃焼ガスとともにブロワーで吸引されつつコアンダブロック構造を有する気流分級機に送られて、コアンダ効果により粗粉と微粉に分級後、それぞれのバグフィルターで捕集される。このときの気流分級機到達時のガス温度は２５０℃であり、コアンダブロック入口の流速は１５０ｍ／ｓで気流分級を行った。分級後微粉側バグフィルターで回収された粉末の特性を表１に示す。
Example 1
Preparation of raw material silica powder A metal silicon powder raw material (average particle size 10 μm) is continuously supplied into a flame formed of LPG-oxygen. The flame-treated product is sucked by the blower together with the combustion gas, sent to an air classifier having a Coanda block structure, classified into coarse powder and fine powder by the Coanda effect, and then collected by each bag filter. The gas temperature at the time of arrival at the airflow classifier at this time was 250 ° C., and the airflow classification was performed at a Coanda block inlet flow velocity of 150 m / s. Table 1 shows the characteristics of the powder collected by the fine powder side bag filter after classification.
フロックキャスト成形法による高密度成形体の作製
得られたシリカ粉が６１．２体積％（７８．７質量％）となるように、分散剤（セルナＤ−７３５、中京油脂製）をシリカ粉に対して１．２０質量％、イオン交換水を加えスラリーを調製した。スラリーは、ボールミル（ポリエチレン製のポット、鉄心入りナイロンボール使用）を用い、１２０ｒｐｍで２４時間回転させ調整した。スラリーの真空脱泡を行った後、ポリエチレン製の型に鋳込んだ。遠心脱泡（３５００ｒｐｍ−１５分）を行い、上澄みを除去した後、相対湿度９０％を保持しながら４０℃で２時間加温し、フロックキャスト固化させた。その後型からはずし、１０５℃で１２時間乾燥させてシリカ粉の成形体を得た。
Preparation of high-density molded body by the flock cast molding method Dispersant (Selna D-735, manufactured by Chukyo Yushi) is used as silica powder so that the obtained silica powder is 61.2% by volume (78.7% by mass). On the other hand, 1.20% by mass of ion-exchanged water was added to prepare a slurry. The slurry was adjusted by rotating at 120 rpm for 24 hours using a ball mill (polyethylene pot, using iron core nylon ball). The slurry was vacuum degassed and then cast into a polyethylene mold. After centrifugal defoaming (3500 rpm-15 minutes) and removing the supernatant, the mixture was heated at 40 ° C. for 2 hours while maintaining a relative humidity of 90% to solidify the flock cast. Thereafter, it was removed from the mold and dried at 105 ° C. for 12 hours to obtain a molded product of silica powder.
この成形体の相対密度は、６５．０％であった。また、この成形体の内部の均一性を液浸透光法を用いて調べたところ、均一性の高いものであった。 The relative density of this molded body was 65.0%. Further, when the uniformity inside the molded body was examined using a liquid permeation light method, the uniformity was high.
透明シリカガラス焼結体の作製および評価
得られた成形体を、シリコニット炉（真空理工製）を用い、１５００℃、保持時間３０分、空気雰囲気下で焼成した。室温まで冷却後、焼結体を取りだし、評価を行った。焼結体の相対密度は、９９．９％であった。紫外可視光透過率を測定したところ、波長が３５０ｎｍの紫外光の直線透過率が厚さ２ｍｍで９４％であった。Ｘ線回折の結果、シリカの結晶相は見いだせなかった。実体顕微鏡で観察すると、５〜２０μｍ前後の直径の丸い気泡と見られる影が、１立方ｍｍあたり１０個程度観察された。更に、電子顕微鏡で気泡形状を観察すると、球状であった。尚、焼結体の不純物量は原料シリカ粉末の不純物量と同等であり、５０ｐｐｍ以下であった。
Production and Evaluation of Transparent Silica Glass Sintered Body The obtained molded body was fired in an air atmosphere at 1500 ° C. for a retention time of 30 minutes using a siliconit furnace (manufactured by Vacuum Riko). After cooling to room temperature, the sintered body was taken out and evaluated. The relative density of the sintered body was 99.9%. When the ultraviolet visible light transmittance was measured, the linear transmittance of ultraviolet light having a wavelength of 350 nm was 94% at a thickness of 2 mm. As a result of X-ray diffraction, a crystalline phase of silica was not found. When observed with a stereomicroscope, about 10 shadows per cubic mm, which were seen as round bubbles with a diameter of about 5 to 20 μm, were observed. Furthermore, when the bubble shape was observed with an electron microscope, it was spherical. The amount of impurities in the sintered body was equal to the amount of impurities in the raw silica powder, and was 50 ppm or less.
（実施例２〜７（実施例３〜６は参考例）、比較例１〜５）
原料粉末種類、分級機入り口の粉体温度、分級機入り口の流速を、表１に示すように変更し（実施例２〜６）、その他は実施例１と同様にして表１に示す粉末特性を有する粉末を得た。
(Examples 2 to 7 (Examples 3 to 6 are reference examples) , Comparative Examples 1 to 5)
The raw material powder type, the powder temperature at the entrance of the classifier, and the flow velocity at the entrance of the classifier were changed as shown in Table 1 (Examples 2 to 6), and the other powder characteristics shown in Table 1 were the same as in Example 1. A powder having was obtained.
原料粉末の不純物量を変更したこと（比較例１〜３）、火炎溶融処理したシリカ粉を分級工程を経ずにバグフィルターで回収したこと（比較例４）以外は実施例１と類似の方法で表２に示す粉末特性を有する粉末を得た。また、市販の球状シリカ粉（商品名「アドマファイン」アドマテックス製）を粒度配合して得たシリカ粉の特性を表２に示す（比較例５）。 A method similar to that of Example 1 except that the amount of impurities in the raw material powder was changed (Comparative Examples 1 to 3), and that the silica powder subjected to flame melting treatment was recovered by a bag filter without going through a classification step (Comparative Example 4). The powder which has the powder characteristic shown in Table 2 was obtained. Moreover, the characteristic of the silica powder obtained by mix | blending particle size of commercially available spherical silica powder (Brand name "Admafine" manufactured by Admatechs) is shown in Table 2 (Comparative Example 5).
尚、表１、表２に示した各粉末の平均球形度はいずれも０．９０以上、シリカ粉末の非晶質率はいずれも９９％以上であった。 The average sphericity of each powder shown in Tables 1 and 2 was 0.90 or more, and the amorphous ratio of the silica powder was 99% or more.
これらの球状シリカ粉を用いて、実施例１と同様の操作を行い、各種焼結体を得た。表１、表２に得られた焼結体の特性を示した。尚、焼結体の不純物量は原料シリカ粉末の不純物量と同等であり、実施例２〜７では、全て５０ｐｐｍ以下であった。 Using these spherical silica powders, the same operation as in Example 1 was performed to obtain various sintered bodies. Tables 1 and 2 show the characteristics of the obtained sintered bodies. In addition, the impurity amount of the sintered compact was equivalent to the impurity amount of the raw material silica powder, and in Examples 2 to 7, all were 50 ppm or less.
（比較例６）
実施例１と同じシリカ粉を原料とし、内径２０ｍｍの円筒状金型と油圧プレス機を用いて圧力２０ＭＰａで一軸加圧成形を行い、成形体を得た。成形体の相対密度は５６％であった。これを、実施例１と同じ条件で焼成したところ、白色の不透明な焼結体を得た。焼結体の相対密度は９６．８％であり、ＸＲＤ分析の結果、結晶質であるクリストバライトが存在し、断面の顕微鏡観察の結果、内部に気泡やクラックが認められた。焼結過程で結晶化が進んだことや、気泡やクラックなどによって、不透明になったと考えられた。
(Comparative Example 6)
The same silica powder as in Example 1 was used as a raw material, and uniaxial pressure molding was performed at a pressure of 20 MPa using a cylindrical mold having an inner diameter of 20 mm and a hydraulic press machine to obtain a molded body. The relative density of the molded body was 56%. When this was fired under the same conditions as in Example 1, a white opaque sintered body was obtained. The relative density of the sintered body was 96.8%. As a result of XRD analysis, crystalline cristobalite was present, and as a result of microscopic observation of the cross section, bubbles and cracks were observed inside. It was thought that it became opaque due to the progress of crystallization in the sintering process, bubbles and cracks.
本発明の透明シリカ焼結体は、透明性、耐熱性に優れるので、各種理化学機器、光学部品、各種耐熱治具、等に使用できる。より具体的には、パイプ、板、坩堝、炉心管、炉内治具、化学薬品用容器、光学ガラス用容器、光学レンズ、分析用セル、熱電対保護管、照明用チューブ、光ファイバー、光ファイバー保持管、外管、等に適用でき、産業上非常に有用である。 Since the transparent silica sintered body of the present invention is excellent in transparency and heat resistance, it can be used in various physics and chemistry equipment, optical parts, various heat-resistant jigs, and the like. More specifically, pipes, plates, crucibles, furnace tubes, furnace jigs, chemical containers, optical glass containers, optical lenses, analysis cells, thermocouple protection tubes, lighting tubes, optical fibers, optical fiber holdings It can be applied to pipes, outer pipes, etc. and is very useful industrially.
本発明の透明シリカ焼結体の製造方法は、透明性、耐熱性に優れる透明シリカ焼結体を、安価に、安定して提供できるので、産業上非常に有用である。 The method for producing a transparent silica sintered body of the present invention is very useful industrially because a transparent silica sintered body excellent in transparency and heat resistance can be stably provided at low cost.
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